Materials for 3d multi-stage method

ABSTRACT

The present invention relates to materials for a multi-stage method for producing one or multiple molded bodies. The materials may be used in a method including constructing one or multiple molded bodies in layers by repeatedly applying particulate material by the 3D printing method; pre-solidifying the molded body; unpacking the pre-solidified molded body and removing unsolidified particulate material, and final solidification of the molded body for achieving a final strength due to the action of thermal energy. The invention also relates to a device which may be used for this method.

CLAIM OF PRIORITY

The present application is a continuation of U.S. patent application Ser. No. 14/435,269 filed on Apr. 13, 2015 which is a 371 of PCT Application serial number PCT/DE2013/000589 filed on Oct. 10, 2013, and claims priority therefrom. This application further claims priority from German Patent Application number DE 10 2012 020 000.5 filed on Oct. 12, 2012. The contents of U.S. patent application Ser. No. 14/435,269, PCT Application PCT/DE2013/000589 and German Patent Application DE 10 2012 020 000.5 are incorporated herein in their entireties by reference.

FIELD OF THE INVENTION

The present invention relates to a multi-stage 3D printing method as well as a device which may be used for this method.

BACKGROUND OF THE INVENTION

A wide range of methods are known for producing molds and foundry cores. Automated machine molding methods are an economical approach in the area of large batches. Tool-less mold production using so-called rapid prototyping methods or 3D printing methods are an alternative to machine molding methods for small to medium-sized series.

Laser sintering methods that permit tool-less manufacturing were developed based on the Croning Method (DE832937), which is known by the name of its inventor, Johannes Croning. According to this method, a molded part is built in layers from particulate material that is coated with a binder. The binding of the individual loose particles is achieved, for example, by applying energy with the aid of a laser beam (EP 0 711 213).

In practice, the solidification described in the prior art is scarcely reached by means of the polycondensation reaction, since process difficulties occur. An exposure to light that is sufficient for developing the final strength would thus result in a severe shrinkage of the binder casing and this, in turn, would cause a process-incompatible distortion of the present layer. The strengths (green strength) of the molded parts produced in this manner are therefore extremely low during removal of the molded parts—also referred to as unpacking—from the loose sand. This causes problems when unpacking and not infrequently results in damage to the molded parts, rendering them unusable. A method has been described for solving this problem during unpacking by using a soldering lamp and thus additionally solidifying the surface with the aid of a soldering lamp. However, this procedure not only requires a great deal of experience, it is also extremely labor-intensive and time-consuming.

The lack of green strengths is due to excessively small or excessively weak binder bridges. If one wishes to engage in distortion-free production, the binder remains excessively viscous and does not form an adequate bridge.

However, a layering method is described in DE 197 23 892 C1, in which Croning sand is printed with a moderating agent, which causes the activation energy of the printed binder-encased Croning sand to be increased or decreased with respect to the unprinted material, and the sand is then exposed to light with the aid of a thermal radiation source. This is intended to cause only the printed or the unprinted areas to be hardened or bound. The finished molded parts are then removed from the unbound sand. However, it has been determined that suitable moderating agents, such as sulfuric acids, are only poorly suited or not suited at all for being printed with the aid of commercial single drop generators. It has also been determined to be disadvantageous that the unsolidified sand is pre-damaged by the exposure to light to such an extent that it may no longer by fully reused in the method. This not only increases the amount of material used but also the costs and is therefore disadvantageous.

A layering method for producing models is described in US 2005/0003189 A1, in which a thermoplastic particulate material is mixed with a powdered binder and printed in layers with an aqueous solvent. The binder should be easily soluble in the aqueous print medium. The models are subsequently removed from the surrounding powder and possibly dried in an oven during a follow-up process for the purpose of increasing the strength.

A layering method for producing investment-cast original models is described in DE 102 27 224 B4, in which a PMMA particulate material, which is coated with a PVP binder, is printed in layers with a mixture of a solvent and an activator for the purpose of dissolving the binder and activating the binder action.

Either the known methods are tool-dependent processes or the known 3D printing processes achieve green strengths that are too low for the efficient and economically advantageous manufacture of molded parts.

DESCRIPTION OF THE INVENTION

Therefore, there was the need to provide a method for the tool-less construction of molded parts in layers, preferably for foundry applications, with the aid of binder-encased particulate material, in which removal strengths or unpacking strengths are achieved which make it possible to reduce or entirely avoid time-consuming and cost-intensive manual work and preferably facilitate machine- or robot-assisted unpacking, or in any case to reduce or entirely avoid the disadvantages of the prior art.

The object of the application is achieved by a method according to claim 1 and a device or device arrangement according to claim 10.

Preferred embodiments are implemented in the subclaims.

In particular, the object is achieved by a method for producing one or multiple molded bodies, the method including the following steps:

a. constructing one or multiple molded bodies in layers by repeatedly applying particulate material by the 3D printing method; b. a presolidification step for achieving a presolidification of the molded body; c. an unpacking step, wherein the unsolidified particulate material is separated from the presolidified molded body; d. a final solidification step, in which the molded body receives its final strength due to the action of thermal energy.

The molded body is preferably subjected to one or multiple additional processing steps. All other methods or work steps known to those skilled in the art may be used. The one or multiple additional processing steps are selected, for example, from the group comprising polishing or dyeing.

In the method according to the invention, the molded body (also referred to as the component) is solidified in the presolidification step to the extent that an unpacking from the unsolidified particulate material is possible, and the molded body essentially retains its shape defined in the 3D printing method. In particular, shrinkage or the like is essentially avoided. The unpacking operation may take place manually or mechanically or in a robot-assisted manner.

Flexural strengths of more than 120 N/cm², preferably more than 200 N/cm², particularly preferably 120 to 400 N/cm² may be achieved in the presolidified molded body (green body) after the presolidification step.

After unpacking, the molded body may again be surrounded by particulate material, which is preferably inert, to thereby be able to support the molded body in the subsequent heat treatment step and better conduct the heat as well as to achieve a uniform heat conduction. Shaking devices may be used to evenly distribute the particulate material.

Flexural strengths of more than 250 N/cm², preferably from 250 to 750 N/cm², preferably more than 750 N/cm², particularly preferably more than 1,000 N/cm², even more preferably more than 1,200 N/cm² may be achieved in the molded body after the final solidification step.

In one preferred embodiment, the method is carried out in such a way that the presolidification step takes place without the application of additional thermal energy.

The presolidification step will preferably take place using a solvent and/or a polymerization reaction.

The final solidification step may preferably take place with the aid of heat treatment. However, other final solidification methods and treatments known to those skilled in the art are also possible.

The component may be supported by inert material during the heat treatment.

Temperatures of preferably 110° C. to 130° C., preferably 130° C. to 150° C., particularly preferably 150° C. to 200° C. are used in the final solidification step.

The temperature at the component is preferably in the time range of 2 to 24 hours; particularly preferably the temperature is maintained over 2 to 5 hours.

Natural silica sand, kerphalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum or glass spheres are used as the particulate material.

The particulate material is characterized by a single-phase coating or casing having one or multiple materials. The coating or the casing may preferably be a binder.

In the method according to the invention, the casing or coating preferably comprises or includes thermoplastic polymers, soluble polymers, waxes, synthetic and natural resins, sugars, salts, inorganic network formers or water glasses.

The solvent preferably comprises or includes water, hydrocarbons, alcohols, esters, ethers, ketones, aldehydes, acetates, succinates, monomers, formaldehyde, phenol and mixtures thereof.

In the method, the binder may contain polymerizable monomers. In one preferred embodiment of the method, the coating or casing contains materials for starting a polymerization with the binder.

The material contained in the casing or coating preferably contributes to the final strength or to the preliminary strength in the presolidification step and to the final strength in the final solidification step.

In the method according to the invention, according to one preferred embodiment, two different materials are contained in the casing or coating, the one material being essentially destined for the presolidification step and the other material essentially being destined for the final solidification step.

The method is thus simplified, may be carried out faster and is thus more economical.

The coating or casing may preferably contain a color indicator which is activated by the binder.

In another aspect, the invention relates to a device or a device arrangement suitable for carrying out the method according to the invention.

The first step of the method according to the invention may, in principle, be carried out as described in the prior art for 3D printing methods. In this regard, EP 0 431 924 B1 and DE102006038858 A1 are cited by way of example. The subsequent unpacking step may be carried out manually but preferably in a mechanically assisted manner. Robot-assisted unpacking is another preferred variant of a mechanical method step according to the invention. In this case, both the unpacking, i.e., the removal of the unsolidified particulate material, and the transfer of the molded part may take place with the aid of computer-controlled gripper arms and extraction units.

The invention is preferably carried out with the aid of a particulate material bed-based 3D printing method. The desired molded body is created during 3D printing by repeated layering. For this purpose, particulate material is applied (leveled) in a thin layer onto a surface. An image according to the section of the desired 3D object is printed using an ink-jet print head. The printed areas solidify and bond to underlying, already printed surfaces. The resulting layer is shifted by the thickness of one layer according to the design of the equipment.

3D printers may be used which lower the layer in the direction of gravity. Machines are preferably used which are designed according to the cycling principle, and the layers in this case are moved in the conveyance direction. Particulate material is now again applied to the building surface. The build process, which involves the steps of coating, printing and lowering, continues to be repeated until the one or more molded body(ies) is/are finished.

The method step of 3D printing and the presolidification step are preferably implemented by selectively printing a solvent onto the binder-encased particulate material. The solvent liquefies the casing. The viscosity is significantly lower than in thermal melting. While the viscosities of polymer melts may be in the range of approximately 10 to 1,000 Pas, a polymer solution may reach a viscosity of a few mPas, depending on the quantity added and the solvent. A viscosity of 2 to 100 mPas is preferred, 2 to 10 mPas is more preferred, 2 to 5 mPas is even more preferred.

When drying the solvent, the fluid mixture withdraws into the contact point between two particles and then leaves behind a strong bridge. The effect may be strengthened by adding polymers to the printing fluid. In this case, suitable method conditions are selected or corresponding components that are necessary for a polymerization reaction are worked into either the solvent or into the coating of the particulate material. All resins or synthetic resins known to those skilled in the art and which are suitable for polymerization, polyaddition or polycondensation reactions may be used. Materials of this type are preferably defined by DIN 55958 and are added to the disclosure of this description with reference thereto.

According to the invention a binder-encased foundry molding material may be used as the particulate material. The casing is solid at room temperature. The particulate material is thus pourable and free-flowing. The material encasing the particles is preferably soluble in the printing fluid that is applied by the ink-jet print head. In a similarly preferred design, the printing fluid contains the casing material or its precursors in the form of a dispersion or solution.

The material present in the printing fluid may likewise preferably belong to a different material group. In one embodiment of the invention, the solvent dissipates into surrounding particulate material or into the atmosphere by means of evaporation. Likewise, the solvent may also react and solidify with the casing material.

The material groups for the particulate material and the casing are varied. The base materials may be, for example, natural silica sand, kerphalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte or corundum. However, other particulate base materials are also generally suitable. The casing may be organic or inorganic. It is applied either thermally, in solution or by mechanical striking or rolling.

In addition to phenol resin, examples of suitable binders are furan, urea or amino resins, novolaks or resols, urea formaldehyde resins, furfuryl alcohol urea formaldehyde resins, phenol-modified furan resins, phenol formaldehyde resins or furfuryl alcohol phenol formaldehyde resin, which may each be present in liquid, solid, granulated or powdered form. The use of epoxy resins is also possible.

For example, encased silica sand having an average grain size of approximately 140 μm, such as the RFS-5000 product from Hüttenes-Albertus Chemische Werke, is particularly preferred. It is supplied with a resol resin casing. In one simple design, an ethanol/isopropyl alcohol mixture may be used as the printing fluid. Predissolved resin may also be added to the printing fluid. One example of this is the Corrodur product from Hüttenes-Albertus. According to the invention, a strength of more than 120 N/cm² results after a time period of 24 hours following the printing process and the addition of 10 wt % liquid binder. Even delicate structures may be quickly unpacked thereby.

A highly concentrated material in the form of predissolved resin of the Corrodur type may furthermore preferably be used as liquid binder for the system. Dioxolane may be used as the solvent additive. Due to the high proportion of resin, molding base materials having a low casing content may be selected. Likewise, untreated sand may be used—with a loss in strength. The design according to the invention in this case may be seen in the complete dissolution of the coating material.

In one particularly preferred embodiment, the materials used in the first method step of 3D printing already include all components required for the final solidification step, preferably binders in the particulate material, which are first bound in the presolidification step using another binding mechanism (physical instead of chemical or vice versa) or other materials (binder in the printing solution) and react/solidify in the subsequent final solidification step in such a way that the advantageous final strength is achieved. It is thus advantageously possible to simplify the different solidification steps in that the particulate material already contains, in the first method step, all materials required for final solidification, and it is possible to achieve the advantageous final strength without introducing additional material in the heat treatment step.

Using the method according to the invention and the device according to the invention, by combining materials and method conditions, the inventors were able to advantageously achieve the fact that an efficient method was provided, which makes it possible to combine work steps, reduce the use of manual steps and thus positively improve the process speed. Using the method according to the invention, it is also possible to achieve flexural strengths in the green body which are sufficient to supply it to a thermal solidification step without damage or other impairments and without the use of tools in the 3D printing method.

Using the method according to the invention and the devices suitable therefor, it is surprisingly possible to include all the materials required for the presolidification step as well as the final heat solidification step in the particulate material. It was astonishing that the combined materials, i.e., the active materials for the presolidification step as well as the final solidification step, did not interact in a way that resulted in interactions between these materials that were detrimental to the method.

By purposefully selecting the materials, the inventors were indeed able to achieve an advantageous effect in preferred embodiments for both the presolidification step and the final solidification step. It has proven to be particularly advantageous that all components required for the method—with the exception of the binder—could be combined into one particulate material, and only one single particulate material may thus be used without the need for additional mixing steps or application steps.

The particularly preferred material combinations according to preferred embodiments are illustrated in the examples. Subcombinations of materials from different examples may also be used together.

DESCRIPTION OF THE FIGURES

FIG. 1 shows particulate material (100), a sand grain (101) being encased with binder (102).

FIG. 2 shows the process of evaporating particulate material (200), to which solvent was added, whereby the particles (200, comprising 201 and 202) are bound and the material is presolidified. The evaporation of the solvent may also be accelerated by the application of heat (203).

FIG. 3 shows the structure of a presolidified molded body (300).

FIG. 4 shows the operation after printing; in this case the solvent begins to penetrate binder coating (402) of particle core (401).

FIGS. 5a through 5d show the evaporation process of the solvent, the mixture concentrating in the contact point (503) between the particles (500) (FIG. 5d ).

As described above, the molded body is formed by binding individual particles (FIG. 3).

The particulate material-based process is based on a particulate material (100) which is encased by a binder (102) (FIG. 1). Casing (102) characteristically has different properties than base material (101). The sand known from the Croning process may be mentioned as an example. In this case, a grain of sand (101) is coated with a novolak resin (102). This resin is melted on and mixed with the sand during the manufacturing process. The sand continues to be mixed until the resin has cooled. The individual grains are separated thereby and a pourable material (100) results.

Base materials having an average grain diameter between 10 and 2,000 μm may be considered as suitable sands for processing in the method according to the invention. Different base materials, such as natural silica sand, kerphalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum and glass spheres are suitable for subsequent use in casting processes.

Binders may be applied in a wide range of materials. Important representatives are phenol resins (resol resins and novolaks), acrylic resins and polyurethanes. All thermoplastics may furthermore be thermally applied to the grains. Examples of materials that may be used according to the invention are polyethylene, polypropylene, polyoxymethylene, polyamides, acrylonitrile, acrylonitrile styrene butadiene, polystyrene, polymethyl methacrylate, polyethyl methacrylate and polycarbonate.

Additionally or entirely without the supply of heat, solvents may be used to coat grains coated according to the invention with a bindable material. Other casings may also be implemented by means of solvents. For example, water glass may be dissolved in water and mixed with sand. The material is subsequently dried and broken. Excessively coarse particles are removed by sieving. Since the dissolution process is reversible, the material thus obtained may be used in the process according to the invention by printing it with water as the printing fluid.

In one preferred embodiment of the invention materials may be provided in casing (102) which demonstrate a reaction with the fluid binder during the dissolution process. For example, starters may be provided for a polymerization. In this manner, the evaporation process of the solvent in the particulate material may be accelerated, since less printing solution needs to escape from the particulate material cake by evaporation. As a result, the molded parts may reach their green strength faster and thus be unpacked from the particulate material earlier.

Since the printed parts do not differ much from the surrounding loose particulate material in a solvent process, it may be sensible to dye the molded parts by introducing a pigment into the print medium. In this case, it is possible to use a color reaction based on the combination of two materials. For example, litmus may be used in the solvent. The base material is mixed with the salt of an acid prior to coating with the binder. As a result, not only is a dyeing possible but also a control of the intensity of the dissolution reaction. If the reactive substance, for example, is in direct contact with the grain of the base material, and if it is protected by the casing, the color indicator shows that the casing was completely dissolved.

The process of evaporating the solvent may also be accelerated by supplying heat (FIG. 2). This may take place by means of convection or heat radiators. The combination of an air draft and heating is particularly effective. It should be noted that if the drying process is too fast, the binder may only be partially dissolved. Optimum values with regard to strength development and unpacking time may be ascertained through tests and variations of the solvent.

A printing fluid is applied to the coated grain in the printing process. In its main function, the printing fluid dissolves the binder casing. In the case of Croning sand, approximately 10 wt % of printing fluid is printed for this purpose. Isopropyl alcohol, for example, is suitable as the solvent. After printing, the solvent begins to penetrate the binder casing (FIG. 4). The concentration of the casing material in the solvent increases. When solvent evaporates, the mixture concentrates in the contact point between the particles (FIG. 5). Additional evaporation causes the casing material in the contact point to solidify. Due to the comparatively low viscosities, a favorable process window results, in contrast to melting processes. With the aid of commercial Croning sand of the Hüttenes—Albertus RFS 5000 type, for example, an unpacking flexural strength of more than 100 N/cm², preferably more than 120 N/cm², is reached. This is sufficient to unpack even large-format, delicate parts safely and distortion-free.

After the removal method step—also referred to as unpacking—the molded parts are supplied to the final solidification step. The molded parts are subsequently supplied to additional follow-up processes. This method step of the invention is preferably carried out in the form of a heat treatment step. Parts made of Croning sand, which are manufactured according to the process according to the invention, may be used as an example. After unpacking, these parts are preferably re-embedded in another particulate material. However, this material does not have a binder casing and preferably has good thermal conductivity. The parts are subsequently heat-treated above the melting temperature of the binder in an oven. In one of the preferred embodiments, the special phenol resin of the casing is cross-linked, and the strength increases significantly. Melting adhesives are generally preferred for this method step of final solidification. The following may preferably be used as base polymers: PA (polyamides), PE (polyethylenes), APAO (amorphous poly alpha olefines), EVAC (ethylene vinyl acetate copolymers), TPE-E (polyester elastomers), TPE-U (polyurethane elastomers), TPE-A (copolyamide elastomers) and vinylpyrrolidone/vinyl acetate copolymers. Other common additives known to those skilled in the art, such as nucleating agents, may be added.

Using the method according to the invention, molded parts having flexural strengths of more than 1,000 N/cm² are produced with the aid of commercial sands

EXAMPLE 1

A Croning sand of the Hüttenes-Albertus RFS 5000 type is used in a layering process. For this purpose, the sand is deposited onto a build plane in a 0.2-mm layer. With the aid of a drop-on-demand print head, the sand is subsequently printed with a solution of isopropyl alcohol according to the cross-sectional surface of the desired object in such a way that approximately 10 wt % is introduced into the printed areas. The build plane is then shifted relative to the layering mechanism by the thickness of the layer, and the operation comprising the layer application and printing starts again. This cycle is repeated until the desired component is printed. The entire operation is carried out under normal conditions. The temperature in the process room should be between 18° C. and 28° C., preferably between 20° C. and 24° C.

Approximately 24 hours must pass before the final layers of sand have developed an adequate strength. The component may then be unpacked, i.e., removed from the surrounding sand and freed of all powder deposits. When printed test bodies are dried in the circulating air oven for 30 minutes at a temperature of 40° C., they demonstrate a flexural strength of 120 N/cm².

The parts are then prepared for the subsequent heat treatment step. For this purpose, they are introduced, for example, into uncoated sand, which is situated in a temperature-resistant container. To ensure a good contact between the part and the supporting sand, vibrations are applied to the container during placement and filling with sand.

Any deformation may be avoided in the manner during the hardening reaction, i.e., the final solidification step, at high temperatures. The component is thus heated in the oven for 10 hours at a temperature of 150° C. After removal from the oven, approximately 30 minutes must again pass until the component has cooled enough to allow it to be handled and removed from the powder bed. Following this process step, the deposits may be removed by sand blasting. Treated bending test bodies demonstrate a flexural strength of 800 to 1,000 N/cm² following this final solidification step.

EXAMPLE 2

A layering process is carried out in a manner similar to the first example. A Croning sand of the Hüttenes-Albertus CLS-55 type is used in this case. For this purpose, the sand is again deposited onto a build plane in a 0.2-mm layer. A solution of 15% Corrodur from Hüttenes-Albertus, 42.5% ethanol and 42.5% isopropyl alcohol is used as the printing fluid.

Approximately 10 wt % of fluid is printed onto the sand.

The flexural strength after unpacking the molded body and completing this first method step, which is also referred to as the presolidification step, is 140 N/cm² in this case. The final flexural strength after the second method step, which is also referred to as the final solidification step, is again 800 N/cm².

EXAMPLE 3

The process for this preferred manufacturing method is carried out in a manner similar to the previous examples. In this case, strengths of 800 N/cm² are achieved using untreated sand as the base. A mixture of 50% Corrodur and 50% dioxolane is used as the binder fluid. 10 wt % are printed. The process takes place at room temperature. The component does not have to be unpacked from the particulate material after printing, since the unencased material cannot be bound by means of thermal energy. Either the entire box or, for example, one printed box may be introduced into the oven to carry out the final solidification step. A sand volume of 8×8×20 cm, which contains a bending test body, is heat-treated in the oven for 24 hours at a temperature of 150°. The strength upon conclusion of the final solidification step is approximately 800 N/cm². A determination of the organic proportion by means of ignition loss determination demonstrates 5 wt %. The material in this case corresponds to the RFS-5000 and CLS-55 products from Hüttenes-Albertus. After the oven process, the parts may be cleaned by sand blasting. 

What is claimed is:
 1. A material system for producing one or more molded bodies, comprising: i) a particulate material having a casing or a coating including a soluble polymer: ii) a printable liquid capable of being selectively printed with an ink jet print head and including a solvent capable of liquefying the soluble polymer for forming bridges between adjacent particles; wherein the particulate material and/or the printable liquid includes a reactive component that reacts at an elevated temperature for achieving a final strength of the molded body.
 2. The material system of claim 1, wherein the casing or coating comprises or includes thermoplastic polymers, soluble polymers, waxes, synthetic and natural resins, sugars, salts, inorganic network formers or water glasses.
 3. The material system of claim 1, wherein the reactive component chemically reacts at temperature of 110° C. to 200° C. to achieve a final strength of the molded body.
 4. The material system of claim 1, wherein the solvent includes water, a hydrocarbon, an alcohol, an ester, an ether, a ketone, an aldehyde, an acetate, a succinate, a monomer, a formaldehyde, a phenol, or any combination thereof.
 5. The material system of claim 1, wherein the casing or coating includes a binder.
 6. The material system of claim 5, wherein the binder includes some or all the reactive component including a polymerizable monomer.
 7. The material system of claim 6, wherein the coating or casing includes an activator for starting a polymerization reaction.
 8. The material system of claim 1, wherein the particulate material includes a core component containing natural silica sand, kephalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum, or glass spheres.
 9. The material system of claim 8, wherein the core component has a grain size of about 140 μm.
 10. The material system of claim 1, wherein the material system includes an inert material for supporting the molded bodies during a reaction at an elevated temperature occurring after formation of bridges between adjacent particles.
 11. The material system of claim 1, wherein the solvent reacts and solidifies with the polymer of the casing or coating.
 12. The material system of claim 6, wherein the particulate material includes a base containing natural silica sand, kephalite, cera beads, zircon sand, chromite sand, olivine sand, chamotte, corundum, or glass spheres; the solvent includes water, a hydrocarbon, an alcohol, an ester, an ether, a ketone, an aldehyde, an acetate, a succinate, a monomer, a formaldehyde, a phenol, or any combination thereof; and the casing or coating comprises or includes thermoplastic polymers, soluble polymers, waxes, synthetic and natural resins, sugars, salts, inorganic network formers or water glasses.
 13. The material system of claim 12, wherein the binder includes a phenol resin, a furan, urea or amino resin, a novolak or resol, a urea formaldehyde resin, a furfuryl alcohol urea formaldehyde resin, a phenol modified furan resin, a phenol formaldehyde resin, a furfuryl alcohol phenol formaldehyde resin, or an epoxy.
 14. The material system of claim 12, wherein a viscosity of the polymer of the casing or coating in the melt state is about is about 10 to about 1,000 Pas, and the viscosity of the polymer in the solvent is 0.002 to 0.1 Pas.
 15. The material system of claim 1, wherein the particulate material has a core of silica sand having a grain size of about 140 μm; the casing or coating includes a resol resin; and the solvent includes isopropyle alcohol, ethanol, or a mixture of ethanol and isopropyl alcohol.
 16. The material system of claim 15, wherein the printable liquid includes a dioxolane additive.
 17. The material system of claim 1, wherein all of the components of the material system are in the particulate material or the printable liquid.
 18. The material system of claim 1, wherein the concentration of the printable liquid is about 10 weight percent, based on the total weight of the particulate material and the printable liquid in the regions printed by the liquid.
 19. The material system of claim 1, wherein the printable liquid includes a dye for identifying the locations that have been printed.
 20. The material system of claim 1, wherein the polymer of the casing or coating includes a polyamide, a polyethylene, an amorphous poly alpha-olefin, an ethylene vinyl acetate copolymer, a polyester elastomer, a polyurethane elastomer, a copolyamide elastomer, or a vinyl pyrrolidone/vinyl acetate copolymer.
 21. The material system of claim 1, wherein the casing or coating includes Corrodur, dioxolane, or both.
 22. The material system of claim 1, wherein the coating or casing contains materials for starting a polymerization with the binder
 23. The material system of claim 1, wherein the coating or casing contains a color indicator which is activated by a binder.
 24. The material system of claim 1, wherein the material system includes a nucleating agent. 